Thermoelectric switch



June 12, 1951 H. c. HANSEN 2,556,582

THERMOELECTRIC SWITCH Filed Dec. 29, 1947 v 4 Sheets-Sheet l B/METfll-L/C INVENTOR. 6% @Wm m June 12, 1951 H. c. HANSEN THERMOELECTRIC SWITCH 4 Sheets-Sheet 2 "F ed Dec. 29. 1947 INVENTOR.

June 12, 1951 H. c. HANSEN THERMOELECTRIC SWITCH 4 .Sheebs-Sheet 5 Filed Dec. 29. 1947 ctrm INVENTOR. min. 3

dktuw (in Patented June 12, 1951 THERMOELECTRI-C SWITCH Hans Christian Hansen, Copenhagen, Denmark, assignor t Dansk Telefonalarm Aktieselskab, Copenhagen, Denmark, a company of Denmark Application December 29, 1947, Serial No. 794,229 In Denmark January 23, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires January 23, 1966 24 Claims.

This invention relates to thermo-switches for fire alarm systems. There is a distinction between two types of such switches of which one is generally called maximal fuse whereas the other type is called differential fuse. The maximum fuse, which in its simplest form consists of an easily fusible soldered connection, operates a switch when the temperature exceeds a certain value, while the differential fuse, which in its principle is based upon the utilization of the difference in expansion or change of form between two bodies diiferently insulated from the surroundings, operates a switch when the speed of the increase of temperature exceeds a certain value.

The present invention relates to thermoswitches of the differential type. In such switches transmission members are provided for transmitting the difierence in movement of the two bodies due to their different temperatures to the switch. It is the object of the present invention to provide a thermo-switch of the type referred to, in which transmission is effected in a simple and reliable manner when the speed of the increase of temperature exceeds a predetermined value.

It is a further object of the invention to provide a thermo-switch in which the electric switch means can be operated responsive to the velocity in rise of temperature without friction.

A further object of the invention is to provide a thermo-switch which will be highly sensitive and remain highly sensitive for a period of many years even when left entirely to itself.

Still a further object of the invention is to provide a thermo-switch in which bimetallic spirals support a floating spindle, in such a manner that bearings, which will involve friction reducing the sensitivity of the switch, are absolutely eliminated.

Other objects will appear as this specification proceeds, reference being had to the accompanying drawing in which Figure 1 is a schematical perspective view illustrating the principle of the thermo-switch according to the invention,

Figure 2 shows the principle of another form of the invention,

Figure 3 shows a convenient construction of the thermo-switch according to Figure 2, the parts being seperated from each other for the sake of clearness,

Figure 4 shows a modification of the switch in Figure 3, and

Figure 5 shows a further embodiment in which the device can also act as maximal fuse.

In Figure 1, l0 and 12 respectively, are two spiral springs of bimetal, of which the spring I2 is enclosed within a housing [4 so that the two springs are diflerently insulated from the surroundings.

The outer ends of the spiral springs are secured to carrier plates (not shown), whereas the inner ends of the springs are connected with each other by a rotatable spindle H5. The turns of the springs are so arranged that the springs tend to rotate the spindle in the opposite directions, as indicated by the arrows.

It will thus be understood that, as long as the springs temperature is constant, the spindle will not move, but as soon as the temperature increases so fast that the heat-insulated spring cannot follow the increase of temperature of the free spring, the spindle will rotate in a clockwise direction.

On the spindle 16 there is secured an arm 18 which carries a magnetic armature 20 situated within the field of a magnet 22. This armature is so adjusted in the magnetic field that the resulting force exerted thereon by the spiral springs balances the attraction of the magnet as long as the difference in temperature of the two springs is below a predetermined value. If the said difierence increases, the spindle will be rotated, as described above, in the direction of the arrow shown at the spring It so as to move the armature in an inward direction in the magnetic field the force of which will thereby assist the spring I0 and suddenly attract the armature so that a set of contacts 2c co-operating with the arm [8 are operated to close or open a circuit.

The embodiment shown in Figure 2 differs from that shown in Figure 1 in that the spiral I0 is divided in two spirals Illa and lllb,'the outer ends of which are secured to carrier plates (not shown), whereas their inner ends are connected with the spindle l6 carrying the spiral [2 at its inner end. The springs Illa, [0b and I2 are wound in the same directions as in Figure 1. The spring [2 is at its inner end connected with a bushing 25 which is rotatable on the spindle l6, and carries at its free end an arm 28. Obviously, the spindle will not be operated for rotation as long as the temperature is constant, and accordingly the arm 28 will not move. If the tempera ture increases so slowly that, in spite of the insulating housing [4, from which the arm 28 extends through a slot 30, no difference in temperature is involved between the two bodies Illa, I01) and I2, respectively, the change of form of the bodies will cause the springs Illa, [0b to rotate the spindle 16 through a small angle in a clockwise direction, as indicated. by the arrows at the springs Illa, llib, but on the other hand the change of form of the spiral spring 22 will cause the arm 23 to be rotated in a counter-clockwise direction, as indicated by the arrow over the spring l2, so that the resulting rotation of said arm will be practically nought.

If, however, the temperature increases so rapidly that the spiral l2 cannot be heated as fast as the spirals lea, lllb, the spindle i6 is rotated in clockwise direction and, since the spiral i2 cannot change its form rapidly enough to prevent this rotation from being transmitted to the arm 28, this arm is moved in a direction opposed to that indicated by the arrow over the spiral 12, whereby the arm 28 is urged with its upper end against a spring it, the bottom end of which is secured to the carrier plates (not shown) and which adjacent its top end carries the armature 29. The spring H3 co-operates with a member 32 for limiting its movements towards the arm 23, and is preferably slightly biased in direction of said member. When the arm 28, due to the difference in change of form of the bodies ifia, lilb and [2, respectively, is urged against the spring iii the armature 29 is moved into the field of the magnet 2'2, and, when the armaturehas been moved sufficiently far into said field it is attracted by the magnet, whereby the spring 68 operates an elec tric switch 24 for opening or closing a circuit.

The initial position of the arm 28 may be adjusted for determining the speed of temperature increase at which the thermo -switch becomes operative by rotating the bushing 28 on the spindle It.

By the division of the one body in two spirals Illa and lilb, and supporting the spindle floating therebetween all friction in bearings is avoided. By further letting the spirals iila and lfib constitute that body which is less insulated relatively .2;

to the surroundings and serve to rotate the spindle and the arm 28, it is possible that the force actuating the switch may be greater than in the case of only one spiral.

In Figure 2 there is shown a practical embodil ment for a switch along the principle outlined in Fig. 1. The same parts as shown and described in connection with Fig. 1 are here referred to by the same reference numerals. The parts shown in Figure 2 are arranged within a housing 34. The lower portion of the housing is divided in three compartments, 3%, 38 and it, of which the two outer ones, 38 and 3B, are provided with venting apertures 52 so that the intermediate compartment it constitutes the insulating housing of the spiral 12,

The housing is further vertically divided in two parts, which are adapted to be assembled by means of a screw 4%. The spirals Mia and E?) are at their outer ends provided with bent portions Mia and llib adapted to be clamped in slots 48a and 48b, respectively, in one part of the housing. The housing is, in its upper portion, formed with a cavity 59 in which the ends of the abutment member 32 for the upper end of the spring it are adapted to be secured, and below the cavity 52 there is provided another cavity or compartment 52 for receiving the magnet. This magnet consists of a permanent magnetic rod 220 having pole pieces 22a and 22b of soft iron, and the compartment 52 is so formed that the magnet with the poles is squeezed therein. The electric switch 24 consists of two switch parts 24a and 24b, respecmeans of projections 56a and 562) provided thereon, is clamped in a cavity 58 immediately below the compartment :32. The contact 241) is provided with an extension 240 adapted to cooperate with the spring [8 to actuate the switch. Under the compartment 58 there is provided another compartment 66 in the bottom of which there is a projection 62 having a screw-threaded hole 64 for receiving a screw 66 which with its end bears adjustably upon the lower portion of the spring i8 for adjusting its bias against the abutment member 32. In the walls 68a and 681) between the compartments 36, 38 and 49 recesses EDA and lib are provided for free passage of the ltloating spindle It.

The middle portion of the spring I3 is provided with an aperture so as to leave only a narrow strip at each side thereof, and the spring is, at its lower end, provided with an upwardly directed tongue E2 on which the screw 66 bears. The spring I8 is further, at its upper end, provided with an indicating member 14 which is made visible in an aperture itat the top of the housing when the armature 26 mounted on the spring is attracted by the magnet 22. The switch is in practice mounted in an inversed position under the ceiling of a room by means of a base plate 18 and it is thus, in case of defects, easy to detect from which of a plurality of such switches the defect comes, because when a switch has been operated, its magnet will retain the armature in the attracted position.

The construction shown in Figure 4 only difiers from that shown in Figure 3 by the armature 18 being pivoted about its centre of gravity by means of springs I9 and 2| secured to projections 6| and 63, respectively, in the housing 34.

By this embodiment, the armature will be less sensitive to vibrations, and the arm 28, by means of which the end of the bimetal spiral I2 actuates the armature, may be much shorter and made of more rigid material, so that the construction will be more robust.

One or both springs 59 and 2| is or are suitably so suspended that their tension may be varied for adjusting the sensitivity of the device.

In Figure 5 there is provided at the exterior end of the spiral I2, instead of a short bent portion 28 in Figure 4;, an elongated member 28a extending upwardly. In Figure 5 the armature is in form of a small magnetic piece of material 20 secured adjacent the top end of a spring It, the bottom of which is secured and clamped in a slot l'l in the housing, and which extends upwardly abutting against the member 32. Preferably the spring I3 is slightly biased in direction of the abutment member 32.

In the bottom of the compartment 60 there is provided a projection 62 having a screw threaded hole M for receiving a screw 66, which at its end bears adjustable upon the lower portion of the spring it for adjusting its bias against the abutment member 32.

As it will appear from Figure 5, the spirals are wound in opposite directions from those shown in Figure 4.

The operation of the switch with respect to its responsiveness to the velocity of increase of temperature corresponds to the way of operation described in connection with Figure 4.

' If the temperature increases so rapidly that the spiral [2 cannot be heated as fast as the spirals ltd, lob, the spindle I6 is rotated in clockwise direction, and, since the spiral l2 cannot change tively, and is mounted on a plate 54 which, by its form rapidly enough to prevent this rotation from being transmitted to the arm 28, this arm is moved in a direction opposite to that indicated by the arrow over the spiral l2, allowing the arm 28 to abut against the spring I8 and thereby moving the armature into the field of a magnet, causing it to operate a contact by the magnetic snap action.

For the sake of clearness the bushing 26 is not shown in Figure 5, and instead the interior end of the spiral I2 is directly mounted on the spindle. It will be understood, however, that in this embodiment the spiral may be arranged on an adjustable bushing as in the case of Figure 4.

There is, however, in Figure 5 a further feature, which is not shown in Figure 4. On the spindle Hi there is provided a bushing 80a, which has a radial arm 82 arranged to cooperate with an abutment 84 projecting sidewardly from the end of the spiral I2.

determined limit, the arm 82 will engage the abutment 84 and thereby operate the switch in the same manner as it would be operated responsive to the velocity of increase in temperature. This operation will be effected also in the event that the velocity of increase in temperature has not been sufiicient to operate the switch.

The maximum temperature, at which the switch should be operated can be adjusted simply by turning the bushing 80 with the arm 82 relatively to the spindle l6.

It will be appreciated that the embodiments shown and described, only illustrate my invention by way of example and may be modified in difierent respects within the scope of the appended claims. Especially it would be understood that in the embodiment shown in Figure 5 the armature can also be substituted by the embodiment shown in Figure 4 in which the armature is supported by springs.

I wish it to be understood that the foregoing description is given as an example only, which may be varied and modified in several respects within the scope of the appended claims.

What I claim is:

l. A thermo-electric switch comprising a supporting structure, at least one primary bimetallie spiral having its outer end attached. to said supporting structure, a floating spindle attached to and carried by the inner end of said primary spiral, a secondary bimetallic spiral having its inner end attached to said floating spindle, means operable responsive to a rotation of said spindle, magnetic snap action type switching means mounted for operation by said means, and means for causing said primary and secondary spirals to be differently heated in response to occurrences to be tested.

2. A thermo-electric switch comprising a supporting structure, at least one primary bimetal lic spiral having its outer end attached to said supporting structure, a floating spindle attached to and carried by the inner end of said primary spiral, a secondary bimetallic spiral having its outer end attached to said supporting structure and having its inner end attached to said float-- ing spindle to maintain the latter in equilibrium by means of said primary and secondary spirals, operating means associated with said spindle, switching means mounted for operation by said operating means, and means for causing said primary and secondary spirals to be difierently heated in response to occurrences to be tested.

3. A thermo-electric switch comprising a supporting structure, a pair of mutually similar primary bimetallic spirals having their outer ends attached tosaid supporting structure to be thereby carried in co-axial relationship, a floating spindle attached to and carried between the inner ends of said primary spirals, a secondary bimetallic spiral having its inner end attached to said floating spindle to be thereby carried tween and in co-axial relationship to said primary spirals, operating means associated with the outer end of said secondary spiral, switch ing means mounted for operation by said operating means, and means for causing said primary and secondary spirals to be differently heated in response to occurrences to be tested.

4. A thermo-electric switch comprising a sup-- porting structure, a pair of mutually similar pri mary bimetallic spirals having their outer ends attached to said supporting structure to be there by carried in co-axial relationship, a floating; spindle attached to and carried between the inner ends of said primary spirals, a secondary bimetallic spiral having its inner end attached to said floating spindle to be thereby carried between and in co-axial relationship to said primary spirals, operating means associated with the outer end of said secondary spiral to move in a path in response to differential heating of said primary and secondary spirals respectively, a movable switching member mounted on said supporting structure independently of said spirals in a position spaced from and in the path of movement of said operating means for operation thereby, and means for causing said primary and secondary spirals to be diiferently heated response to occurrences to be tested.

5. A thermo-electric switch comprising a supporting structure, a pair of mutually similar pri-- mary bimetallic spirals having their outer ends attached to said supporting structure to be thereby carried in co-axial relationship, a floating spindle attached to and carried between the inner ends of said primary spirals, a secondary bimetallic spiral having its inner end attached to said floating spindle to be thereby carried be tween and in co-axial relationship to said primary spirals, operating means associated with the outer end of said secondary spiral to more in a path in response to diiierential heating said primary and secondary spirals respectiveiy, a magnetic snap action type switching member mounted on said supporting structure independently of said spirals in a position spaced from and in the path of movement of said operating means for operation thereby, and means for causing said primary and secondary spirals to be diiferently heated in response to occurrences to be tested.

6. A thermo-electric switch comprising a sup" porting structure, a pair of mutually similar primary bimetallic spirals having their outer ends attached to said supporting structure to be thereby carried in co-axial relationship, a floating spindle attached to and carried between the inner ends of said primary spirals, a secondary bimetaL- lic spiral having its inner end attached to said floating spindle to be thereby carried between 7 or and in co-axial relationship to said primary spirals, operating means associated with the outer end of said secondary spiral to move in a path in response to differential heating of said pri mary and secondary spirals respectively, a spring biased magnetic snap action type switching mem ber mounted on said supporting structure independently of said spirals in a position spaced from and in the path of movement of said operating means for operation thereby, and means for causing said primary and secondary spirals to be diiierently heated in response to occurrences to be tested.

'7. A fire alarm switch comprising a supporting structure, a pair of similar primary bimetallic spirals in equal heat exchange relationship with the surrounding atmosphere, said primary spirals being wound in the same winding direction and having their outer ends attached to said sup porting structure to be thereby carried in co axial relationship, a floating spindle attached to and carried between the inner ends of said spirals, a secondary bimetallic spiral in different heat exchange relationship with the surrounding atmosphere, said secondary spiral wound in the same winding direction as said primary spirals and having its inner end attached to said floating spindle to be thereby carried between and in co-axial relationship to said primary spirals, operating means associated with the outer end of said secondary spiral, to move in a path in response to differential heating of said primary and secondary spirals, respectively, a mayable switching member mounted on said sup porting structure independently of said spirals in a position normally spaced from and in the path of movement of said operating means for operation thereby, means producing a snap action magnetic field acting on said switching member in a direction away from said operating means, spring biasing means acting on said switching member in a direction towards said operating means, and a fixed stop for limiting the movement of said switching member under the influence of said spring biasing means.

8. A fire alarm switch comprising a supporting structure including walls defining three compartments in mutual alignment, ventilation openings in the two outer compartments for communication with the atmosphere, the intermediate compartment being closed towards the atmosphere, a pair of similar primary bimetallic spirals having their outer ends attached to said supporting structure to be thereby carried in coaxial relationship in the respective ones of said outer compartments, a floating spindle attached to and carried between the inner ends of said spirals and passing freely through said intermediate compartment, a secondary bimetallic spiral having its inner end attached to said fioating spindle to be carried in said intermediate compartment in co-axial relationship to said primary spirals, operating means associated with the outer end of said secondary spiral and switching means mounted for operation by said operating means.

9. A fire alarm switch comprising a supporting structure including walls defining three compartments in mutual alignment, ventilation openings in the two outer compartments for communication with the atmosphere, the intermediate compartment being closed towards the atmosphere, a pair of similar primar bimetallic spirals having their outer ends attached to said supporting structure to be thereby carried in co-axial 8 relationship in the respective ones of said outer compartments, a floating spindle attached to and carried between the inner ends of said spirals and passing freely through said intermediate compartment, a secondary bimetallic spiral similar to said primary spirals and having its inner end attached to said floating spindle to be carried in said intermediate compartment in coaxial relationship to said primary spirals, operating means to move in a path in response to differential heating of said primar and secondary spirals, respectively, associated with the outer end of said secondary spiral, a movable switching member mounted on said supporting structure independently of said spirals in a position normally spaced from and in the path of movement of said operating means for operation thereby, means producing a snap action magnetic field acting on said switching member in a direction away from said operating means, spring biasing means acting on said switching member in a direction towards said operating means, and a fixed stop for limiting the movement of said switching member under the influence of said spring biasing means.

10. The 'thermo-electric switch, as set forth in claim 1, in which said means operable responsive to a rotation of said spindle comprises an elongated armature member, springs adjustably attached to said supporting structure at spaced locations and extending in opposite directions to floatingly carry between them said armature member to pivot about its center of gravity, a switch operating member associated with the exterior end of said secondary bimetallic spiral in a position to operate said elongated armature member responsive to a rotation of said floating spindle, and said magnetic snap action type switching means mounted for operation by said armature member.

11. The thermo-electric switch, as set forth in claim 1, in which said means operable responsive to a rotation of said spindle comprises an elongated armature member, springs attached at one end to said supporting structure, and carrying at their other ends said armature member in a position to pivot about its center of gravity, a switch operating member associated with the exterior end of said secondary bimetallic spiral in a position to operate said elongated armature member responsive to a. rotation of said floating spindle, and said magnetic snap action type switching means mounted for operation by said armature member.

12. The thermo-electric switch, as set forth in claim 1, in which said means operable responsive to a rotation of said spindle comprises an elongated armature member, springs for carrying said armature to pivot about its center of gravity, a switch operating member associated with the exterior end of said secondary bimetallic spiral in a position to operate said elongated armature member responsive to a rotation of said floating spindle, and said magnetic snap action type switching means mounted for operation by said armature member.

13. The thermo-electric switch, as set forth in claim 1, in which said means operable responsive to a rotation of said spindle comprises an elongated armature member movably supported by said supporting structure, a switch operating member associated with the exterior end of said secondary bimetallic spiral in a position to operate said elongated armature member responsive to a rotation of said floating spindle, and said magnetic snap action type switching means mounted for operation by said armature member.

14. The thermo-electric switch, as set forth in claim 1, in which said means operable responsive to a rotation of said spindle comprises an elongated armature member operable responsive to a rotation of said spindle, and said magnetic snap action type switching means mounted for operation by said armature member.

15. The thermo-electrio switch, as set forth in claim 1, in which said means operable responsive to a rotation of said spindle comprises an operating member associated with the exterior end of said secondary spiral, an elongated armature member, means for floatingly supporting said armature member to pivot about its center of gravity in a position to be operated by said operating member responsive to a rotation of said spindle, and said magnetic snap action type switching means mounted for operation by said armature member. 7

16. The thermo-electric switch, as set forth in claim 1, in which said means operable responsive to a rotation of said spindle comprises an operating member associated with the exterior end of said secondary spiral, a further operating member associated with said spindle, an elongated armature member, means for supporting said armature member in a position to be operated by either of said operating members responsive to a rotation of said spindle, and said magnetic snap action type switching means mounted for operation by said armature member. 1

17. The thermo-electric switch, as set forth in claim 1, in which said means operable responsive to a rotation of said spindle comprises operating means associated with the outer end of said secondary spiral, further operating means associated with said floating spindle, and said switching means mounted for operation by either of said operating means.

18. The thermo-electric switch, as set forth in claim 1, in which said means operable responsive to a rotation of said spindle comprises operating means associated with the outer end of said secondary spiral to move in a path in response to differential heating of said primary and secondary spirals, respectively, further operating means associated With said floating spindle to move in a path in response to rotation of said spindle, and a movable switching member mounted on said supporting structure independently of said spirals in a position spaced from and in the path of movement of said operating means for operation thereby.

19. The thermo-electric switch, as set forth in claim 1, in which said means operable responsive to a rotation of said spindle comprises operating means associated with the outer end of said secondary spiral to move in a path in response to difierential heating of said primary and secondary spirals, respectively, an elongated switch operating member, spring means extending from said supporting structure to carry said switch operating member to pivot about its center of gravity independently of said spirals in a position spaced from and in the path of movement of said operating means for operation thereby.

20. The thermo-electric switch, as set forth in claim 1, in which said means operable responsive to a rotation of said spindle comprises first operatin means associated with the outer end 01 said secondary spiral to move in a path in respense to differential heating of said primary and secondary spirals, respectively, further operating means associated with said floating spindle to move in a path in response to rotation of said spindle, a movable switch operating armature mounted on said supporting structure independently of said spirals in a position spaced from and in the path of movement of said first operating means for operation thereby, and said magnetic snap-action type switching means mounted for operation by said armature.

21. The fire alarm switch, as set forth in claim 8, which includes further operating means associated with said floating spindle, and in which said switching means are mounted for operation by either of said operating means.

22. The fire alarm switch, as set forth in claim 8, in which said operating means move in a path in response to differential heating of said primary and secondary spirals, respectively, which includes an elongated armature structure mounted on said supporting structure independently of said spirals in a position to pivot about its center of gravity and having one end spaced from and in the path of movement of said operating means, and in which said switching means are of the magnetic snap action type which is mounted for operation by said armature.

23. The fire alarm switch, as set forth in claim 8, in which said operating means move in a path in response to diiferential heating of said primary and secondary spirals, respectively, which includes further operating means associated with said floating spindle to move in a path in response to rotation of said spindle, which also includes an elongated armature structure mounted on said supporting structure independently of said spirals in a position to be operated by either of said operating means, and in which said switching means is of the magnetic snap action type and mounted for operation by said armature.

24. The fire alarm switch, as set forth in claim 9, in which said structure includes walls defining adjacent one of its ends one cavity and adjacent the other of its ends a second cavity forming the said three compartments disposed in mutual aligmnent, the former receiving the magnetic means of said switch.

HANS CHRISTIAN HANSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS McCabe Mar. 7, 1939 

